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Started work on v1.19.1: Debugger improvements

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Jeff Parsons 2015-08-19 13:06:43 -07:00
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blog/2015/07/17/README.md
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@ -88,13 +88,28 @@ Update for August 13, 2015
---
PCjs v1.18.8 has made a little more progress running Windows 95 Setup, but CAB decompression still fails almost
immediately. To monitor DOS calls until the first 36-byte read of PRECOPY1.CAB, try the following breakpoints and
start the machine, using the PCjs Debugger *input* field next to the **Enter** button:
immediately. To monitor DOS calls until the first 36-byte read of PRECOPY1.CAB, try setting the following
breakpoint and then starting the machine, using the PCjs Debugger *input* field next to the **Enter** button:
m dos off
bp 1ED4:16B4 "let fn=ah;dos;if fn!=3f||cx!=24"
bp FDC8:422A "if fn==3f;di ds:dx;db ds:dx lcx;h;else"
g
Alternatively, you can hard-code those commands into the Debugger component of the machine.xml file; eg:
<debugger id="debugger" messages="fault|tss|int" commands='m dos off;bp 1ED4:16B4 "let fn=ah;dos;if fn!=3f||cx!=24"'/>
Once the 36-byte read is hit, you'll probably want to stop on the next instruction that examine those bytes,
by using a memory read breakpoint:
br ds:dx
and you also might want to change the first breakpoint to stop on *any* file read, and add a second breakpoint
to dump the initial contents of those reads:
bp 1ED4:16B4 "let fn=ah;dos;if fn!=3f"
bp FDC8:422A "if fn==3f;di ds:dx;db ds:dx;h;else"
In the current machine, `1ED4:16B4` is the DOS INT 0x21 entry point and `FDC8:422A` is the corresponding IRET.
The first breakpoint sets an internal variable, `fn`, to the value of the **AH** register on entry, so that the second
breakpoint can check the value on exit.